1. Field of the Invention
The disclosed technology relates to a sensor for sensing the presence of at least one fluidum in an adjoining space, to the use of a sensor for sensing at least one fluidum in an adjoining space and a method for making such sensor.
2. Description of the Related Technology
Sensors of that kind are already known to the person skilled in the art. The article “Development of GaN-based Micro Chemical Sensor Nodes” by Nicholas Prokopuk, Kyung-Ah Son, Thomas George and Jeong S. Moon published in IEEE sensors 2005, for example, describes a sensor for sensing the presence of at least one fluidum, in this case a gas, in an adjoining space. The sensor comprises HEMT with a two-dimensional electron gas (2DEG) layer stack comprising an AlGaN layer and a GaN layer. A gate overlays at least part of the 2DEG layer stack and electrostatically controls electron density of a 2DEG in the 2DEG layer stack. Molecules interfere with the upper surface of the 2DEG layer stack, in this case the surface of the AlGaN layer, and have an influence on the 2DEG in the 2DEG layer stack. The sensor also comprises a source and a drain electrode for contacting the 2DEG for measuring an electric characteristic of the 2DEG, more in particular the current between the source and the drain.
However, the gate of the sensor for controlling the electron density of the 2DEG must be kept small in order to provide a sufficiently large surface area between the source and the drain above the 2DEG where the fluidum, in this case gas, molecules can alter an electric characteristic of the 2DEG, such as for example the current between the source and the drain, for example by being adsorbed by the surface area between the source and the drain above the 2DEG. As this limits the dimensions of the gate, which is provided for controlling the electron density of the 2DEG, the control of the electron density in the 2DEG is often insufficient.
Moreover, it has been found that the gate, even with limited dimensions, still reduces the area of the surface where the molecules can influence the 2DEG therefore limiting the sensitivity of the sensor, especially at very low concentrations of the molecules of the fluidum which is desired to be detected.